The present invention relates to an automatic hydraulic advance for a diesel engine injection pump of the type described in the above referenced parent application. In particular, the present invention concerns an improvement which allows a further increase in the operational stability of the device, even when it is subjected to drive forces which are large, variable or pulsating.
The principle of the device according to the parent application consisted in interposing a mechanism of irreversible operation between the casing 8 of the drive pinion and the hub 7 of the pump camshaft, this irreversible mechanism consisting of two pistons 11 and 12, controlled by a variable hydraulic pressure. The irreversible mechanism consists of an angular assembly including respectively, a lateral oblique ramp 13 and 14, on each piston 11 and 12, bearing on a roller 9 and 10 of the casing 8. Thus any variation controlled by the hydraulic pressure causes without difficulty a sliding of the pistons 11 and 12 in the desired direction, in order to cause the desired angular displacement between the pump camshaft and its drive pinion. On the other hand, the irreversibility of the mechanism makes it impervious to shocks caused on the rollers 9 and 10 by the camshaft, due to the operation of the pump.
Naturally, so that this device operates in a satisfactory manner, it is necessary to maintain the inclined ramps 13 and 14 of the pistons 11 and 12 in contact with and the rollers 9 and 10 of the drive pinion. In the parent application, this retention of contact is insured by two return springs 36 (FIG. 4 of the parent application) permanently stretched between the hub 7 and the casing 8 of the pump.
Experience has shown that if the strength of the operational forces and the speed of rotation of the pump are increased, it is possible to reach a threshold above which the springs 36 become insufficient to maintain contact between the inclined ramps 13, 14 and the rollers 9 and 10 at all times.